run_tests fails with unclear error when wrong path to test is specified

[Sebastian Kalinowski]

In fuel-web, when running selected test using run_tests.sh scipt and path to nonexistent file is specified, unclear error message is thrown:

# ./run_test.sh -t some/fake/path.py
./run_tests.sh: line 604: $1: unbound variable

It's because there is no checking if readlink returned anything: https://github.com/stackforge/fuel-web/blob/09089099c369a13b47badab6a077c5edc353e942/run_tests.sh#L136-L137

There should be a error instead, like:
"File some/fake/path.py not found"

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/141076

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/141076
Committed: https://git.openstack.org/cgit/stackforge/fuel-web/commit/?id=c3df5c2b52491296f74a329f668c9bd4085192b8
Submitter: Jenkins
Branch: master

commit c3df5c2b52491296f74a329f668c9bd4085192b8
Author: Julia Varigina <email address hidden>
Date: Thu Dec 11 07:43:14 2014 -0800

    Print descriptive error message if test file does not exist

    Added verification that test file or directory exists for the command:
    run_tests.sh -t <test file>

    If a test file (or directory) does not exist, run_tests.sh prints error message:
    ERROR: File or directory <test file> not found
    and exits with status 1

    Change-Id: Ia0b11efe434daf7f040943ea8622bad496074563
    Closes-Bug: #1397916